Catalytic converter devices used in motor vehicles to reduce emissions of certain fuel combustion products may be somewhat less efficient at operating temperatures below their so called light-off temperature. Typically, following start-up of a cold engine, a short period of time passes before the light-off temperature is reached. In order to reduce unwanted emissions, it is desirable to use a hydrocarbon (HC) trapping device to remove certain hydrocarbon combustion products from the engine's exhaust gas stream during the period following a cold engine start when the primary catalyst has not yet reached its light-off temperature. To reduce these emissions, HC trapping devices have been proposed to capture and hold at least selected HC combustion production until a later time when they can be recycled and eliminated by the more fully heated engine or operational catalytic converter. To recycle the accumulated hydrocarbons, the trapping device is purged after the cold starting period, the stored hydrocarbons being released and routed to the catalyst or to the engine for further processing and conversion to a less harmful chemical form.
It is desirable in certain applications to ensure that such HC trapping devices continue to operate properly during the life of the vehicle. While the performance of the primary catalyst is typically monitored by sensing the oxygen storage ability of the catalyst and relating this property to the catalyst's ability to convert hydrocarbons, HC trapping devices do not store oxygen as catalysts do, and the systems and methodologies utilized for catalysts cannot be used for HC trapping devices. A need exists, therefore, for methods and apparatus capable of effectively monitoring the performance of HC trapping devices to ensure their continued proper operation.
It is accordingly a principal object of the present invention to accurately and inexpensively monitor the performance of hydrocarbon trapping devices of the type used to reduce hydrocarbon emissions during cold engine startup conditions.